A technology (Japanese Patent Application Laid-Open Publication No. 2002-230533) exists, which determines a get-into-bed event by detecting a movement of a human body from a floor area into abed area in a way that passes through a frame border of an image captured from upward indoors to downward indoors, and determines a leaving-bed event by detecting a movement of the human body from the bed area down to the floor area.
Another technology (Japanese Patent Application Laid-Open Publication No. 2011-005171) exists, which sets a watching area for detecting that a patient lying down on the bed conducts a behavior of getting up from the bed as an area immediately above the bed, which covers the patient sleeping in the bed, and determines that the patient conducts a behavior of getting up from the bed if a variation value representing a size of an image area of a deemed-to-be patient that occupies a watching area of a captured image covering the watching area from a crosswise direction of the bed, is less than an initial value representing a size of the image area of the deemed-to-be patient that occupies the watching area of a captured image obtained from a camera in a state of the patient lying down on the bed.
In recent years, there has been an annually increasing tendency of accidents that watching target persons such as inpatients, care facility tenants and care receivers fall down or come down from beds and of accidents caused by wandering of dementia patients. A watching system is, as exemplified in the document described above, developed as a method of preventing those accidents. The watching system is configured to detect behaviors of the watching target person such as a get-up state, a sitting-on-bed-edge state and a leaving-bed state by capturing an image of the watching target person with a camera installed indoors and analyzing the captured image. This type of watching system presumes the behavior of the watching target person on the basis of an analyzed result of two-dimensional image captured by the camera. Therefore, this leads to acquisition of a result of the behavioral presumption not suited to a state of the watching target person in a space in reality (which will hereinafter be termed a “real space”) as the case may be.